The optical networks of today typically use static paths which may take from minutes to days to provision, and which often remain unchanged for days to months. The paths, which are typically set up by a service provider using central management systems, are often contiguously concatenated. In such traditional synchronous optical networks (SONET) and synchronous digital hierarchy (SDH) networks, failure of a constituent path will cause the entire contiguously concatenated path to fail as well. The service providers charge their customers for the availability and transmission quality of these static paths, where availability and transmission quality are measured using SONET/SDH performance monitoring capabilities.
The next generation of optical networks have recently introduced virtually concatenated paths which allow an arbitrary number of SONET and SDH elementary paths (such as VT-1.5s, STS1s and the like) to be logically grouped in virtual concatenation groups (VCGs). The VCG members are transported as synchronous payload envelopes across the SONET/SDH network and recombined at the VCG termination sink. Furthermore, next generation optical networks have recently begun offering a capability to dynamically create and delete paths, and to increase or decrease bandwidth of existing paths, without the intervention of a central management system.
The VCGs are further enriched by the link capacity adjustment scheme (LCAS), which allows dynamic reconfiguration of VCGs, including dynamic changes in the bandwidth of VCGs. This capability is used to maintain part of the transmission capacity of a VCG even if several constituent elementary paths experience failures. Using the link capacity adjustment scheme, failed channels are automatically removed from the VCG without loss of data, and in the absence of network errors.
In such dynamically switched networks, a paradigm of fixed bandwidth per path is no longer required. As a result, service providers are beginning to charge customers not only for availability and transmission quality of a provided path, but for the bandwidth made available to those customers in a provided path. Since these dynamic bandwidth changes are out of the control of the service provider (i.e., occurring in a decentralized manner without using service provider management systems), bandwidth monitoring performance parameters associated with dynamic bandwidth allocation are not currently supported by SONET/SDH networks.
The SONET/SDH performance monitoring is currently implemented using various combinations of element and network management systems that are used to measure the availability and transmission quality of a path; however, monitoring of path bandwidth variability is not currently supported. Thus, any autonomous changes in a switched network (such as new path setup, existing path failure, bandwidth adaptations and the like) currently result in notifications such as alarms and log file entries. The service provider management systems use these notifications received from the network elements in order to charge customers for bandwidth made available to the customers over time.
Using this notification information, management systems can estimate the available bandwidth over time; however, this approach has some serious drawbacks. First, the bandwidth estimate is inaccurate since it is not directly measured by the network elements, but rather is derived from events that occur in the network. Furthermore, the bandwidth estimate is unreliable as it depends on a permanent management connection between network elements and the management systems. If this connection is temporarily unavailable, or the management system itself is temporarily unavailable, the data required to estimate the bandwidth provided to a customer is lost, and the required billing data cannot be calculated.